Need of flat panel display for computer rises accompanied with spreading of information terminals. Moreover, electronic paper or digital paper as a thin, light and easily mobile displaying medium is needed because the chance of providing information in a form of electronic signals instead of paper medium is increased accompanied with the progress of information system.
In the planar displaying apparatus, the displaying medium is generally constituted by the use of an element applying liquid crystal, organic EL or electrophoresis. In such the displaying medium, technology in which an active driving element (TFT element) is principally applied for obtaining a uniformity of the brightness and a high rewrite speed of the image. In usual displays for computer, for example, the TFT elements are formed on a glass substrate and the liquid crystals or the organic EL elements are sealed.
A semiconductor such as a-Si (amorphous silicon) and p-Si (polysilicon) is employable for the TFT element. The TFT element is formed by successively laminating the silicon semiconductor and a metal layer according to necessity for forming a source electrode, a drain electrode and a gate electrode. A production process utilizing vacuum such as a spattering process is usually needed for producing the TFT element.
In the production of the TFT element, the production process including a vacuum process using a vacuum chamber has to be repeatedly applied for forming the constituting layers. Consequently, the costs for equipment and running the production become very high. For the TFT element, processes such as a vacuum deposition, doping and photolithography should be repeatedly performed for each of the layers. Therefore, the element is formed on the substrate through several tens processes. In a semiconductor portion making the important point of switching action, plural kinds of layer such as a p-type semiconductor layer and an n-type semiconductor layer are laminated. In such the processes for producing the silicon semiconductor, the change of the equipment corresponding to the requirement of large-sizing of the displaying image is difficult because a largely changing in the design of the production apparatus such as the vacuum chamber is necessary.
The material of the substrate is limited to one having a resistivity against heating in the processes since the usual production processes for the TFT using silicon include a process performed at high temperature. Consequently, glass is only practically usable. Therefore, the displaying apparatus becomes one which is heavy, lacking in the flexibility and easily broken by falling when the displaying apparatus is constituted by the usual TFT elements. Such the properties caused by forming the TFT elements on the glass substrate are not suitable for satisfying the requirements for the light mobile thin display accompanied with the progress of the information system.
Besides, studying on organic semiconductor material having high charge transfer ability is aggressively progressed. Such the compounds are expected as an element of an organic laser oscillation element (cf., for example, Non-patent Document 1) additionally to the charge transfer material of the organic EL element, and that of organic thin film transistor such as those reported in various reports (cf., for example, refer Non-patent Document 2).
It may be made possible by realization of such the organic semiconductor devices that the simplification of the production process by applying a vapor deposition under vacuum or low pressure at a relatively low temperature. Moreover, it may be possible that the semiconductor can be produced by using a solution by suitably improving the molecular structure of the compound so that the production by a printing process including an ink-jet method can be realized by making the organic semiconductor solution to an ink. Though it may impossible to produce the semiconductor element by such the low temperature process by using the usual silicon type semiconductor material, it may be possible with respect to the device employing the organic semiconductor. Therefore, the limitation on the heat resistivity of the substrate is alleviated and, for example, the TFT element may be possible to be formed on a transparent resin substrate plate. When the TET elements can be formed on the transparent resin substrate plate and the displaying materials can be drove by the TFT elements, the display will be made to one lighter in the weight, higher in the flexibility than those of the usual one and is hardly or difficultly broken by falling.
However, the organic semiconductors studied for realizing such the TFT element are only limited kinds of compound, for example, an acene-type compound such as pentacene and anthracene (cf., for example, Patent Document 1), a phthalocyanine including lead phthalocyanine, a low molecular weight compound such as perylene and its tetracarboxylic acid derivative (cf., for example, Patent Document 2), an aromatic oligomer typically such as a hexamer of thiophene so-called as α-thienyl or sexithiophnen (cf., for example, Patent Document 3), a compound of naphthalene or anthracene symmetrically condensed with a 5-member aromatic heterocyclic ring (cf., for example, Patent Document 4), a mono-, oligo- and poly-thienylenopyridine (cf., for example, Patent Document 5) and a conjugate polymer such as polythiophene, poly(thienylene vinylene) and poly(p-phenylene vinylene). Accordingly, development of a semiconductor composition employing a novel charge transferable material showing high carrier mobility is demanded. Japanese Patent Tokkai 2003-292588, U.S. Patent Opened Application Nos. 2003/13658, 2003/160230 and 2003/164495 describe as follows. “The mechanical strength of a logical integrated circuit element for microelectronics is largely improved and the using life time of it can be prolonged by employing a polymer TFT. However, the polythiophene semiconductors are mostly instable in air because which is doped by oxygen in the atmosphere so that the electro conductance of it is increased. As a result of that, the off current of the device produced from such the materials is increased, and the on/off ratio of the electric current is decreased. Therefore, the materials cause problems of that the materials should be exactly controlled so as to prevent the oxidation doping or to minimize the effect of the oxidation doping during the processing of the materials and the production of the device by eliminating the oxygen in the atmosphere. Consequently, an electronic device is demanded, which has high resistivity against oxygen and shows relatively high ON/OFF ratio of the electric current.” And the various means for resolving such the problem are proposed (for example, cf. Patent Documents 6 to 11 and Non Patent Document 4). However, the level of the improvement is insufficient and further improvement is desired.                Patent Document 1: Tokkai Hei 5-55568        Patent Document 2: Tokkai Hei 5-190877        Patent Document 3: Tokkai Hei 8-264805        Patent Document 4: Tokkai Hei 11-195790        Patent Document 5: Tokkai 2003-155289        Patent Document 6: Tokkai 2003-261655        Patent Document 7: Tokkai 2003-264327        Patent Document 8: Tokkai 2003-268083        Patent Document 9: Tokkai 2004-186695        Patent Document 10: Tokkai 2003-264327        Patent Document 11: Tokkai 2003-268083        Non-patent Document 1: “Science” vol. 289, p. 599, (2000)        Non-patent Document 2: “Nature” vol. 403, p. 521, (2000)        Non-patent Document 3: “Advanced Material” 2002, No. 2, p. 599, (2000)        Non-patent Document 4: “J. Am. Chem. Soc.” 126, 11, 3378 (2004)        